There are three basic types of end dump trailers, frameless, full frame and quarter frame. On a frameless dump trailer, the suspension and wheels are rigidly connected to the body so that when it dumps only the rearmost wheels stay on the ground and the trailer body rotates about the point where the tires contact the ground. As a result, the rear end of the trailer drops down during dumping. On a full frame dump trailer, there is a long frame that spans the entire length of the trailer from the coupler plate in front (where the trailer is linked to a truck) to the rear hinge (where the trailer body is connected to the frame). This frame remains horizontal and connected to the truck during dumping while a hydraulic cylinder lifts the front of the trailer body. As a result, all of the tires remain in contact with the ground throughout the entire dump cycle and the rear end of the trailer does not drop down. On a quarter frame dump trailer, there is a partial frame that extends from the rear hinge (where the trailer body is connected to the frame) to slightly forward of the front axle of the trailer. A mechanical linkage is utilized to hold down the front end of this frame which would otherwise rise upward due to instability caused by the weight of the trailer body and payload acting eccentrically to the supports for the frame. As a result, a quarter frame trailer is able to dump similarly to a full frame trailer where all wheels maintain contact with the ground and the rear end does not drop down.
Of these three basic types of end dump trailer, the frameless, the full frame and the quarter frame, only with the quarter frame is it impractical to use an air ride suspension.
In most attempts to use air ride suspensions on quarter frame trailers, because of imperfections in the physical geometry of the quarter frame linkage, the magnitude of the forces generated in the various components is so great that for said components to safely resist these forces, the components' size and weight are sufficiently large as to effectively preclude their use.
In some applications, the quarter frame trailer has certain advantages over either full frame or frameless trailers. When compared to a full frame trailer with an equal length hydraulic cylinder, a quarter frame trailer provides a higher dumping angle and a fairly significant weight advantage, thereby allowing it to carry a greater payload and remain in compliance with highway load limits. When compared to a frameless trailer, a quarter frame trailer provides equal or better stability while dumping and the rear end of the trailer does not drop down during the dumping process. Because of these advantages and the fact that a majority of customers prefer an air ride suspension to a spring suspension, it is extremely desirable to provide a quarter frame trailer with an air ride suspension.